Sandblasting devices for directing a stream of abrasive particles under pressure against a surface have been known for a number of years. Conventionally, such devices operate to entrain sand or a similar abrasive in a stream of air under pressure which is then ejected from a nozzle and directed against a surface to be cleaned or abraded. Spent abrasive particles and debris are then withdrawn by vacuum and returned to a collection and recycling assembly. The abrasive material is separated from the debris and recycled for further use. Examples of such sandblasting systems are illustrated by U.S. Pat. Nos. 2,483,176 and 2,597,434 to L. H. Bishop et al, 2,766,557 to G.M. Pollard, 2,770,924 to W.H. Mead et al, and 4,045,915 to N.J. Gilbert et al.
As illustrated by the cited patents, most sandblasting devices involve the use of a single nozzle positioned within a shroud or hood for directing abrasive material against a surface, but some sandblasting assemblies known to the prior art have incorporated a plurality of material directing nozzles. For example, U.S. Pat. Nos. 1,829,599 to H.E. McCrery and 3,517,416 to B.E. Baldwin et al illustrate multiple nozzle units wherein abrasive material provided by gravity from a storage reservoir is distributed to the input ends of a plurality of conduits leading to output nozzle units. U.S. Pat. No. 2,628,456 to R. R. Berg illustrates a sandblasting device wherein sand entrained in a stream of air is fed to a divider which splits the stream into branches which are fed through separate hoses to a plurality of nozzles. These known multiple nozzle units all require the use of a plurality of separate input conduits leading to the output nozzles for the air and abrasion material, thereby making multiple nozzle devices bulky and difficult to manipulate. More importantly, however, is the fact that even metering or distribution of air and abrasive media flow through the separate nozzles does not occur with prior multiple nozzle units.
For sandblasting, uniform distribution of air and sand to a plurality of nozzles is normally not required, as it is not imperative to maintain the integrity of the surface being abraded. For many applications, however, where the surface integrity must be maintained, soft cleaning of a sensitive surface is desirable. For example, the removal of a wax build-up on a vinyl tile floor requires that the wax be removed while the integrity of the soft vinyl is maintained, and often chemical cleaning has been the only effective way to clean soft surfaces without damage. In instances where soft cleaning with abrasives is used, the necessity to accurately control both the pressure and the content of the abrasive particle stream has led to the use of single nozzle units where such control can be maintained. Such a unit is illustrated by U.S. Pat. No. 4,646,480 to R.F. Williams. The rapid cleaning of a large area is severely inhibited by use of a single nozzle but uneven flow through multiple nozzles will at best, result in an unevenly cleaned surface showing marks caused by abrasive material impacting from different nozzles.